Fix horizontal_wrapping row height after using text_edit_multiline (#8000)

* [x] I have followed the instructions in the PR template

This PR have two commits:
* **First commit** - introduction of tests and their canonization image.
Expected behaviour is that `horizontal_wrapped_multiline_row_height`
would match `horizontal_wrapped_multiline_row_height_reference`, but it
doesn't. There is a bug in `horizontal_wrapped` that breaks line height
after using `text_edit_multiline`.
* **Second commit** - fix. You can see that
`horizontal_wrapped_multiline_row_height` now looks like
`horizontal_wrapped_multiline_row_height_reference` (although it's not a
perfect match, upd: found, this is because of this issue:
https://github.com/emilk/egui/issues/4921).

I have used LLM to help me with this PR (codex + claude code).

BTW, I'm using horizontal_wrapped with end_row instead of vertical +
horizontal alternation, because I automatically generate my UI through
some complex interactions between elements in my code, and it's can be
that my `horizontal` starts in one function, and ends in another.
Something like `begin_horizontal`/`end_horizontal`/`get_current_layout`
would be very handy, related to
https://github.com/emilk/egui/issues/1004.

Also, I would like indent to be supported in `horizontal_wrapped`, or
also, to have `indent_start`/`indent_end`. This is why I used
`monospace("| ")` in my example, it simulates my use-case.

crates/egui/src/layout.rs

@@ -623,12 +623,24 @@ impl Layout {
         if (self.is_vertical() && self.horizontal_align() == Align::Center)
             || self.horizontal_justify()
         {
-            frame_size.x = frame_size.x.max(available_rect.width()); // fill full width
+            // For wrapping layouts, fill the current column width, not the entire layout width.
+            let width = if self.main_wrap {
+                region.cursor.width()
+            } else {
+                available_rect.width()
+            };
+            frame_size.x = frame_size.x.max(width); // fill full width
         }
         if (self.is_horizontal() && self.vertical_align() == Align::Center)
             || self.vertical_justify()
         {
-            frame_size.y = frame_size.y.max(available_rect.height()); // fill full height
+            // For wrapping layouts, fill the current row height, not the entire layout height.
+            let height = if self.main_wrap {
+                region.cursor.height()
+            } else {
+                available_rect.height()
+            };
+            frame_size.y = frame_size.y.max(height); // fill full height
         }
 
         let align2 = match self.main_dir {
@@ -791,14 +803,14 @@ impl Layout {
                     let new_top = region.cursor.bottom() + spacing.y;
                     region.cursor = Rect::from_min_max(
                         pos2(region.max_rect.left(), new_top),
-                        pos2(INFINITY, new_top + region.cursor.height()),
+                        pos2(INFINITY, new_top),
                     );
                 }
                 Direction::RightToLeft => {
                     let new_top = region.cursor.bottom() + spacing.y;
                     region.cursor = Rect::from_min_max(
                         pos2(-INFINITY, new_top),
-                        pos2(region.max_rect.right(), new_top + region.cursor.height()),
+                        pos2(region.max_rect.right(), new_top),
                     );
                 }
                 Direction::TopDown | Direction::BottomUp => {}

tests/egui_tests/tests/regression_tests.rs

@@ -279,3 +279,88 @@ fn warn_if_rect_changes_id() {
         "Should warn when a widget rect changes Id between passes"
     );
 }
+
+#[test]
+fn horizontal_wrapped_multiline_row_height() {
+    let mut harness = Harness::builder().with_size((350.0, 300.0)).build_ui(|ui| {
+        ui.style_mut().interaction.tooltip_delay = 0.0;
+        ui.style_mut().interaction.show_tooltips_only_when_still = false;
+
+        let mut string = String::new();
+
+        ui.horizontal_wrapped(|ui| {
+            ui.monospace("| ");
+            let _ = ui.button("A");
+            let _ = ui.button("B");
+            ui.end_row();
+
+            ui.monospace("| ");
+            let _ = ui.button("C");
+            let _ = ui.button("D");
+            let _ = ui.button("E");
+            ui.end_row();
+
+            ui.monospace("| ");
+            ui.text_edit_multiline(&mut string);
+            ui.end_row();
+
+            ui.monospace("| ");
+            let _ = ui.button("F");
+            let _ = ui.button("G");
+            ui.end_row();
+
+            ui.monospace("| ");
+            let _ = ui.button("H");
+            let _ = ui.button("I");
+            let _ = ui.button("K");
+            ui.end_row();
+        });
+    });
+
+    harness.snapshot("horizontal_wrapped_multiline_row_height");
+}
+
+#[test]
+fn horizontal_wrapped_multiline_row_height_reference() {
+    let mut harness = Harness::builder().with_size((350.0, 300.0)).build_ui(|ui| {
+        ui.style_mut().interaction.tooltip_delay = 0.0;
+        ui.style_mut().interaction.show_tooltips_only_when_still = false;
+
+        let mut string = String::new();
+
+        ui.vertical(|ui| {
+            ui.horizontal(|ui| {
+                ui.monospace("| ");
+                let _ = ui.button("A");
+                let _ = ui.button("B");
+            });
+
+            ui.horizontal(|ui| {
+                ui.monospace("| ");
+                let _ = ui.button("C");
+                let _ = ui.button("D");
+                let _ = ui.button("E");
+            });
+
+            ui.horizontal(|ui| {
+                ui.monospace("| ");
+                ui.text_edit_multiline(&mut string);
+            });
+
+            ui.horizontal(|ui| {
+                ui.monospace("| ");
+                let _ = ui.button("F");
+                let _ = ui.button("G");
+            });
+
+            ui.horizontal(|ui| {
+                ui.monospace("| ");
+                let _ = ui.button("H");
+                let _ = ui.button("I");
+                let _ = ui.button("K");
+            });
+        });
+    });
+
+    harness.snapshot("horizontal_wrapped_multiline_row_height_reference");
+}

tests/egui_tests/tests/snapshots/horizontal_wrapped_multiline_row_height.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ef21b42f90401f6b85685e1cc37d07970b38d2b40394f53bbde5bd4f0d54fb95
+size 5340

tests/egui_tests/tests/snapshots/horizontal_wrapped_multiline_row_height_reference.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5025f4cb528ae5edc387149f1d14523ab4b93058f0862e775a1c2276a3e77af6
+size 5377